1. Technical Field
The invention concerns improved trick mode playback, and more particularly to improvements in the trick mode playback of audio soundtrack associated with a video segment played back at a faster than normal speed.
2. Description of the Related Art
DVD trick modes can include speedup or slowdown of normal playback to either search for a specific location on the disc or to look at details of a particular scene that would be missed at normal speed. By convention, normal playback speed can be denoted as 1xc3x97. Both audio and video trick modes are possible and both can be found on commercially available DVD players. However, conventional methods for playback of audio at fast or slow speed have proved to be problematic. The advancement of digital signal processors and especially audio digital signal processors that are used in currently available products have created the possibility for more sophisticated real-time processing for improved audio trick modes.
One problem with the use of video trick modes concerns the treatment of audio corresponding to a trick playback video segment. For example, when a user speeds up or slows down a program video segment, the corresponding audio segment that is played back can be distorted. Typically, audio samples in the audio segment can be shifted to higher frequencies during a fast trick mode, and to lower frequencies during a slow trick mode. The fast trick modes that increase the playback speed by a factor of between about 1.5 to 3 times as compared to normal playback will tend to cause human speech to sound higher in pitch. This higher pitched audio playback, the chipmunk effect, can be annoying and in many instances may be unintelligible to a listener. Conversely, slow frequency trick modes can produce a low frequency wobble that may be understandable but not aurally pleasing.
In order to obtain the most useful audio playback during video trick modes as described herein, it is also necessary to consider the nature of the particular trick mode. For example, while it may be possible to utilize various techniques to provide intelligible audio for 1.5xc3x97 or 2xc3x97 trick modes, such techniques may provide unsatisfactory results when the trick mode involves playback at 5xc3x97 or 10xc3x97. At such high rate playback speeds, any attempt to play back audio content in synchronism with the video may result in unintelligible speech due to the very rapid rate at which words would need to be presented.
To avoid the various types of audio artifacts resulting from DVD trick modes, conventional DVD players will often mute the audio during trick modes. However, this is not an entirely satisfactory solution as the audio may be of interest in such modes. Accordingly, it would be advantageous if a DVD player could playback audio in a manner that overcomes the limitations of the prior art and achieve a desirable and aurally pleasant playback of audio during video trick modes.
The invention concerns a method and apparatus for playing audio programming during a faster than 1xc3x97 speed video trick mode playback of a video presentation. The method begins with the step of retrieving from a storage medium information for producing at least a video portion and a corresponding audio portion of a presentation. The audio portion of the presentation, like most audio sound tracks, includes periods of relative silence. For example, these may occur between words or between dramatic pauses in the dialogue. Audio gating is used to selectively gate the audio portion of the presentation to remove at least a portion of the periods of relative silence. Finally, a remaining part of the audio portion of the presentation is concatenated for playback to remove any gaps after the portion of the periods of relative silence have been removed.
The removing step can include selectively removing a percentage portion of the periods of relative silence based on a selected video trick mode playback speed. According to one aspect of the invention, the removing step can further include determining an optimized percentage portion of each period of silence that must be removed in order to synchronize the audio portion and the video portion for playback after the concatenating step. The removing step can also include increasing the percentage portion of the periods of silence that are removed in order to achieve a faster video trick mode playback speed.
The gating step can further include selectively setting a gating threshold based on a selected video trick mode playback speed. An optimized gating threshold can be selected that is necessary to synchronize the audio portion and the video portion for playback after the concatenating step. In general, increasing the gating threshold will facilitate audio playback during a faster video trick mode speed.
The invention also concerns an apparatus for playing an audio track during a faster than 1xc3x97 speed video trick mode playback of a video presentation. The apparatus can include a storage medium reader for retrieving from a particular storage medium the information for producing at least a video portion and a corresponding audio portion of a presentation. As noted above, the audio portion of the presentation typically will comprise periods of relative silence. An audio gate is provided for selectively gating the audio portion of the presentation to remove at least a portion of the periods of relative silence. The output of the audio gate can be communicated to an audio processor for concatenation after the periods of relative silence have been removed.
The invention can further include a processor for selectively determining a percentage portion of the periods of relative silence to be removed based on a selected video trick mode playback speed. According to one aspect of the invention, the processor can determine an optimized percentage portion necessary to synchronize the audio portion and the video portion for playback after concatenation. In general, the processor will selectively increase the percentage portion of the periods of silence for removal for a faster video trick mode playback speed.
The processor can also selectively set a gating threshold based on a selected video trick mode playback speed. According to one embodiment, the processor selectively determines an optimized gating threshold necessary to synchronize the audio portion and the video portion for playback after the concatenating step. In general, the processor will selectively increase the gating threshold for a faster video trick mode playback speed.